Not printing thin walls

I'm using a .8mm nozzle and created a model with .8mm wall thickness in some areas. The thin walls run straight vertical from bed. I am printing on RostockMax running 1.5.3 MatterControl and using MatterSlicer

Part of the thin wall is a cylinder shape, part of it is flat wall shape. The cylinder shaped walls do print, but, the thin flat walls, MatterSlicer doesn't print them at all.

I will try making the walls thicker, but, I wanted the walls thin so i can more easily cut them off and remove them. I am using them as support. In this particular model, when i let the program generate support, the support is too tough and difficult to remove. I am printing with PETG with single extruder, so support and model would be in PETG. I created thin walls to that they will support a flat overhang higher up in the model. But, matterslicer isn't printing the walls.

thanks, that works better then making the shell 1 mm thick... never had that issue with Slic3r, but, so far i am liking MatterSlicer - the bed leveling works... i was having a nightmare with Repeiter firmware getting it to map the bed. Got a Zprobe, but, could never get it just right. I used the 7 point, then the 13 point on MatterControl, and i can lay down a flat 1st layer all round. My Rostock Max is 2 1/2 years old, and now that i have updated the arms, got an all metal E3D head, and now switched to MatterControl, it is working better then it ever did - like i got a whole brand new printer